Human angiotensinogen has been purified by a six step procedure and the amino acid sequence of the first 13 residues of the amino terminal end determined. It is proposed to extend the sequence work so as to obtain the sequence of the first 20 to 24 residues. The reaction between purified human renin and purified human angiotensinogen will be characterized by kinetic studies. The inhibitory effect, if any, of purified human alpha 1-antitrypsin and human alpha 2-macroglobulin on the reaction of purified human renin with purified human angiotensinogen will be determined. In addition to the predominant form of angiotensinogen present in human plasma, a high molecular weight is also present. The amount of high molecular angiotensinogen present in the following groups will be determined: low renin essential hypertension, renovascular hypertension, and pregnancy induced hypertension.